Smoking kills 480,000 Americans annually, exacerbates myriad diseases, and costs billions in healthcare and productivity losses.1-5 Numerous barriers exist to accessing traditional treatment (e.g., costs, traveling to and scheduling appointments, other logistics).6 Text messaging is an extremely popular communication method. Over 80% of all Americans use text messaging,7 giving it unparalleled reach across the population. Smoking cessation interventions delivered through text messaging have shown promise as an effective way to reach and treat the broad population of smokers, while eliminating the many barriers associated with traditional treatment approaches. However, most existing commercially available programs have not been empirically tested, were not developed with end-user participation, are not evidence-based, and/or do not address cognitive and behavioral variables that have been shown to enhance smoking cessation in clinical trials. This direct-to-phase II (PAR-14-088) application builds on our pilot work in which Live InspiredLLC and our research partners developed T2Q (formerly Text-2-Quit) a smoking cessation intervention delivered through text messaging. T2Q is a unique program with a number of features that provide superior support and service compared to existing text message quit smoking products (see section 2.4). T2Q is 100% accessible through text messaging provides medication support for quitting smoking, an integrated social support network and live counseling. In this phase II project we will add functionality to accommodate use of multiple forms of nicotine replacement therapy (NRT) to our existing NRT medication support system, following FDA guidelines.8,9 We will then conduct a rigorous test of the efficacy of T2Q among 280 adult smokers and examine smoking outcomes compared to controls at 3 and 6 months follow up. We will examine changes in smoking-related attitudes and behaviors among T2Q users to identify strengths and any potential weaknesses that may affect T2Q's impact on smoking outcomes. We will examine the quality of social interactions within the T2Q integrated social support network and their role in promoting smoking abstinence. We will also conduct interviews with study participants in the T2Q arm to enhance our understanding of the user's experience with T2Q. Results of this trial will demonstrate the efficacy of T2Q - providing important credibility needed for successful commercialization. This research will also provide important data for possible enhancements to improve consumer appeal prior to commercialization. This proposal finalizes development and testing of a unique, highly scalable intervention that can reach a U.S. market comprised of over 34 million adult smokers who use text messaging, and provide them with effective, evidence-based treatment. Text messaging enjoys near-market saturation and is a widely preferred method of communication with deep penetration across diverse groups. Wide availability of an attractive and effective smoking cessation program such as T2Q, may exert a powerful, sustained impact on public health.